Field
The present invention relates to a light-emitting device comprising a light-emitting device and a manufacturing method thereof.
Discussion
Light-emitting devices fabricated as individual chips are packaged so that they are electrically connected to printed circuit boards, power supplies or control means. When a chip is packaged, it is protected from the external environment, and its electrical connection with an external terminal is achieved smoothly. In particular, a light-emitting device functions to allow the light generated by supply of electric power to be easily emitted to the outside and also functions to allow the heat generated to be dissipated to the outside.
With the recent advancement of technologies for the formation of compound semiconductor single crystals and the control of dopants, high-output light-emitting devices have been realized. The realization of high output of light-emitting devices requires high power supply and causes problems associated with the dissipation of the heat generated.
Particularly, when the heat generated in a light-emitting device is not smoothly dissipated to the outside, it may result in the deterioration of the light-emitting device. In an attempt to solve this problem, ceramic materials or metals have recently been used as package materials.
Ceramic materials have the advantage of blocking external heat, because they have low heat transfer properties. However, these ceramic materials have a problem in that they do not easily dissipate the heat generated in packages. In addition, the ceramic materials have a problem in that a separate reflective material needs to be provided below a light-emitting chip so that the light generated in packages is easily emitted to the outside.
The use of a metal material as a package material has an advantage in that high heat transfer properties can be ensured. However, the use of a polymer material as a molding material makes it difficult to ensure heat dissipation properties, even when a frame made of a metal material is used.
FIG. 1 is a cross-sectional view showing a light-emitting device according to the prior art.
Referring to FIG. 1, the light-emitting device according to the prior art has a frame 1, a molded portion 3, a chip mounting portion 5 and a lens portion 7.
The frame 1 is made of a metal material, and the molded portion 3 is provided on the peripheral portion of the frame 1. The molded portion 3 forms the sidewall of the light-emitting device and extends vertically. The molded portion 3 includes a polymer material different from the metal material forming the frame 1.
Also, the chip mounting portion 5 is provided in the internal space defined by the surface of the frame 1 and the molded portion 3. The chip mounting portion 5 may be a chip or a chip-mounted substrate. The chip mounting portion 5 is electrically connected to the frame 1 by wire bonding or surface mounting.
Further, the lens portion 7 is provided on the upper end of the molded portion 3. The lens portion 7 is made of a transparent material and bonded to the molded portion 3.
The above-described configuration has a problem in that, because the molded portion 3 forming the sidewall of the light-emitting device cannot easily dissipate the heat generated in the package, the heat transfer properties of the light-emitting device are deteriorated. Moreover, the decrease in heat transfer to the outside leads to deterioration in the light emitting properties of the light-emitting chip. In addition, because the molded portion 3 forming the sidewall of the package is made of a black polymer material, it cannot sufficiently reflect the light emitted.
Particularly, when the light-emitting device emits light in the ultraviolet region, the light reflecting properties of the package will be deteriorated due to the frame 1 made of a metal material or the molded portion 3 made of a black polymer material, and the reliability of the light emitting device will be deteriorated due to the low heat transfer properties of the package. In addition, when heat is generated in the light-emitting device, the lens portion 7 can be detached from the molded portion 3, because it is made of a material having an expansion coefficient different from that of the molded portion 7.
Additionally, if the frame 1 is completely made of a metal such as Al in order to increase the reflectivity, a chip or a submount is mounted on the frame 1 using an Ag paste containing an organic material such as epoxy or silicone, because soldering is impossible as a Sn-based solder is not bonded onto the Al frame.
However, when the chip or the submount is mounted using the Ag paste containing the organic material as described above, the organic material will be influenced by the light (particularly UV light) from the chip for a long period of time, and thus the Ag paste will be delaminated from the frame 1, or the chip or the submount will be delaminated from the Ag paste, resulting in deterioration in the reliability of the device.
In addition, a conventional surface-mount device (SMD) type ceramic package having a cavity is manufactured by mounting a light-emitting device in the cavity, and then bonding a window-type or hemisphere-type glass lens directly to the upper end of the cavity. Alternatively, instead of placing the glass lens on the upper end of the cavity, a polymer such as a fluoropolymer or a silica-based polymer is injected into the cavity by a molding process so as to function as a lens while protecting the light-emitting device.
However, the conventional ceramic package comprising the glass lens placed directly on the upper end of the cavity is not satisfactory in terms of optical efficiency and light intensity, because light extraction is performed through the lens spaced away from the light-emitting device. Moreover, the ceramic package comprising the polymer lens filled in the cavity in place of the glass lens has a shortcoming in that the light transmittance is somewhat low, because the thickness of the polymer is inevitably thick. Particularly, in the case of light-emitting devices that emit UV C light (deep UV light), the optical efficiency is significantly reduced as the thickness of the polymer becomes thicker.
Further, in the case of STEM packages, a lens-integrated cap is bonded to a head by eutectic bonding to protect the light-emitting device. However, the STEM packages are not difficult to produce using automatic systems, and thus cannot be produced in large amounts. In addition, because the package surface is plated with Au having low reflectivity, a relatively low light intensity is shown even when the same light-emitting device is applied.
In recent years, in order to solve the costly problem of conventional STEM packages, which results from high material costs and production costs, there have been attempts to use inexpensive packages such as ceramic packages or general plastic packages as LED packages for UV light.
For example, a lens can be attached to a package body using an adhesive after mounting a LED in the cavity of the package body. The cavity is sealed with the adhesive so as to prevent water from penetrating from the outside. The cavity is closed by the package body, the lens and the adhesive, and thus the penetration of external water and the like into the cavity is prevented. However, during the attachment of the lens, the lens can be detached from the package body by compressed air produced in the cavity, thus causing adhesion failure. For example, when the lens is pressed against the package body using a lens holder with the adhesive interposed therebetween, compressed air is produced in the cavity. When the lens holder is removed, the lens can be detached from the package body by the compressed air. In addition, during curing of the adhesive, air in the cavity can be expanded, and the lens can be detached from the package body due to an increase in air pressure in the cavity.